The large H.E.S.S. II Cherenkov telescope in Namibia at dusk

Gamma-ray burst · 9 October 2022

GRB 221009A

The brightest gamma-ray burst ever recorded, nicknamed the BOAT. H.E.S.S. limits help constrain how its afterglow produced high-energy photons.

Our part

H.E.S.S. follow-up campaign over more than a week; the very-high-energy upper limits were published in ApJ Letters.

Follow-up, step by step

9 October 2022
Fermi-GBM and Swift-BAT
The burst is detected and localised.
T0 to T0 + 2 days
H.E.S.S.
No observations possible, as the full Moon makes the sky too bright.
11 October 2022
H.E.S.S.
Observations start and continue for more than a week, under clouds and high aerosol levels.
2023
Publications
No significant signal; stringent upper limits on the very-high-energy flux.

Chart comparing the prompt emission of GRB 221009A with five earlier record-holding long gamma-ray bursts

Papers

H.E.S.S. Follow-up Observations of GRB 221009A

H.E.S.S. · 2023 · Astrophys.J.Lett. 946 L27

Rocking the BOAT: the ups and downs of the long-term radio light curve for GRB 221009A

Rhodes et al. · 2024 · Mon.Not.Roy.Astron.Soc. 533 4435